Antennas for use in satellite television reception only (TVRO) systems, are well known in the art. These dish-type antennas are used by a homeowner to receive satellite broadcast television programs from any one of a number of satellites in geosynchronous orbit over the equator. Each antenna includes as major components the dish or reflector which is oriented towards the satellite, and a feed which is located at the focal point of the dish. The dish or reflector ranges in size from approximately a four-foot diameter to an eleven-foot diameter and the antennas are generally mounted for rotational movement atop a pole which is anchored in a concrete pad or the like.
One of the reasons for the size of these main reflector dishes is that is is an important factor in determining the quality of the reception. The cross-sectional area of the main reflector dish projected into a plane defines the aperture of the dish, and the larger the aperture, the better the reception, all other things being equal. Therefore, a larger dish size adds to performance, but it creates problems focusing the dish on individual satellites, keeping the dish focused on the desired satellite, and also moving it from satellite-to-satellite at the operator's command. As the wind picks up velocity, the antenna has a tendency to shift, drift or oscillate, a phenomenon known as mispointing, such that the television reception is degraded. Therefore, it is important to be able to accurately, reliably, and rigidly point and move the dish in spite of the wind.
In each antenna's installation, there are three adjustments which must be made to properly orient the antenna to track the arc of satellites. These include elevation, declination, and azimuth. Elevation is the angle that the axis of rotation forms with respect to horizontal. Declination represents the angle that the center axis of the dish forms with respect to the axis of rotation. Azimuth represents the horizon-to-horizon movement of the antenna as necessary to move from one satellite to another. The azimuth movement is generally motorized and is the one adjustment made by the homeowner after the antenna is installed. The elevation and declination adjustments are initially made, and should remain unchanged after the antenna is properly installed.
The declination adjustment is typically achieved by one of two schemes in the prior art. In a first scheme, an elongated threaded bolt extends from a point on the dish to part of its back-up structure, and the dish may be tilted by moving a double-nut connection between the threaded bolt and the dish. This scheme suffers from several drawbacks. First of all, the center of mass of the entire reflector dish is altered as the dish is tilted to adjust the declination. Because of the necessity to stabilize the antenna in the wind, a declination adjustment which alters the center of mass of the dish requires that supporting structure be necessarily designed to handle the entire range of declination adjustment. Obviously, some declination adjustments will be better stabilized than others, and the antenna will suffer from reduced performance depending upon the particular required declination. Still another disadvantage of this design is that the declination adjustment provided by the threaded bolt does not exhibit a great deal of vernier control. This makes it somewhat difficult to achieve the proper declination upon installation.
Still another scheme utilized in prior art antennas is a swivel connection made at the very center of the dish to a supporting structure. This requires that the entire weight of the dish be held in place as the nuts are tightened in the swivel joints, something that can be very difficult to do given the weight of the dish. Furthermore, the pivoting arrangement provides a constant torque in a direction tending to loosen the declination adjustment such that its reliability over time is not great. The weight of the dish, and the forces placed on it by the wind all have a tendency to loosen the declination adjustment and shift the antenna dish off the arc of satellites. This results in a degradation of the received signal.
To solve these and other problems in the prior art, the inventors herein have succeeded in designing and developing an antenna system which represents a significant improvement over those designs heretofore known. In the design of the present invention, the main reflector dish has a back-up structure with an upper and lower curvilinear surface. These curvilinear surfaces rest against an upper and lower pad, with slots and holes cut in the surfaces and pads to permit the insertion of nut and bolt assemblies. Thus, the full weight of the antenna dish rests on an upper and lower pad surface, and the nuts may be loosened on the bolt assemblies to permit the whole antenna dish to slide against the pads to change the declination adjustment. As can be appreciated, this provides a significant improvement over the declination adjustments found in the prior art. First of all, this declination adjustment is integral with the antenna reflector dish and its pivotal mount. There is a frictional engagement between the curvilinear surfaces and the pads which more evenly distributes the load of the antenna on its mount to thereby diminish the potential for slippage of the antenna dish after it is once adjusted. Because of the sliding action of the antenna dish with respect to the pads, virtually the same center of mass is maintained across the entire declination adjustment which reduces the deleterious effect on wind stability as in the prior art. The entire weight of the antenna dish is supported by the pads, and the nut and bolt assemblies may be only slightly loosened to permit the easy sliding movement of the antenna dish on the pad surfaces until the proper declination has been achieved. At that time, the antenna dish may be locked in place by tightening the nut and bolt assemblies. Thus, it is a simple matter to adjust the declination with the invention of the present design as it does not require an operator to support the weight of the main reflector dish while tightening the declination adjustment structure.
The principal advantages and features of the present invention have been described. However, a greater understanding and appreciation for the invention may be obtained by referring to the drawings and detailed description of the preferred embodiment which follows.